Poliadenilação alternativa em espécies da Aliança Tabebuia sob seca

Abstract

Alternative polyadenylation (APA) is a co-transcriptional mechanism that generates alternative transcripts, which can regulate plant gene expression in response to biotic/abiotic stresses. However, in plant species, this mechanism remains poorly understood. Thus, the objective of the study was to analyze APA patterns in four species of ipês, two from Cerrado (Handroanthus ochraceus and Tabebuia aurea) and two from forest (Handroanthus impetiginosus and Handroanthus serratifolius) submitted to drought. For this, RNA-seq data from the four species under two treatments (under drought and control) were used as input to the APAtrap tool, which identifies potential APA sites and their utilization dynamics between treatments. Genes that presented FDR (False Discovery Rate) < 0.05 and PD (Percentage Difference) > 0.2 were considered as having significant differential use of polyadenylation sites (DE-APA). H. ochraceus was the species that presented the highest number of DE-APA genes (3,530) and H. impetiginosus the lowest (120). H. serratifolius and T. aurea had similar numbers of genes with DE-APA: 368 and 169, respectively. H. ochraceus shared 102 and 103 DE-APA with T. aurea and H. serratifolius, respectively. There were no DE-APA genes shared among all four species. Genes with DE-APA were classified as CR-APA, when APA was located in the coding region; and as UTR-APA when it was located in the 3'UTR of the gene. H. impetiginosus presented 61 UTR-APA and 59 CR-APA; H. serratifolius had 197 CR-APA and 171 UTR-APA; T. aurea with 228 CR-APA and 141 UTR-APA; finally, H. ochraceus presented 1,089 CR-APA and 2,441 UTR-APA. Previous work indicates that genes with shorter 3'UTR end tend to be more expressed. Only in H. ochraceus there was a significant association between the size of the 3'UTR and the level of gene expression. In this species, among genes with shorter 3'UTR (proximal APA), 59% were up-regulated, while 62.5% of the UTR-APA genes with longer 3'UTR (distal APA) were down-regulated. Fisher's exact test detected Gene Ontology (GO) categories enriched only among the DE-APA genes of H. ochraceus. These GO categories were involved in transcriptional regulatory pathways, protein transport/localization and macromolecule catabolic processes. These results indicate that the response to drought can be regulated by APA in ipê species. Among the studied species, H. ochraceus seems to use this co-transcriptional regulation mechanism more intensively. However, further studies are needed to understand the consequences of APA on the final expression of genes in this species.